Subject: Re: Warning from ring buffer code (Was: Re: linux-next: tip tree 
 build warning)
From: Steven Rostedt <srostedt@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Christopher Li <sparse@chrisli.org>,
       Jaswinder Singh Rajput <jaswinder@kernel.org>,
       Ingo Molnar <mingo@elte.hu>, Stephen Rothwell <sfr@canb.auug.org.au>,
       Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>,
       linux-next@vger.kernel.org, linux-kernel@vger.kernel.org,
       linux-sparse@vger.kernel.org, Josh Triplett <josh@freedesktop.org>,
       Frederic Weisbecker <fweisbec@gmail.com>
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Organization: Red Hat
Date: Mon, 14 Sep 2009 14:31:16 -0400
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On Mon, 2009-09-14 at 20:23 +0200, Peter Zijlstra wrote:
> On Mon, 2009-09-14 at 14:17 -0400, Steven Rostedt wrote:
> > Frederic, how big can one of those events get. The ring buffer (and
> > TRACE_EVENT) allow up to almost a page size, which is very hefty for the
> > stack. This code needs to either be rewritten or we need to set a limit
> > to the size of a profile entry.
> 
> Yeah, that needs to get a re-write.. I've complained about this when it
> went in.

One answer is to create a per cpu buffer that is big enough to hold the
data needed. Then you can disable interrupts an use it without worry.

If you need to also handle NMIs, then create a per_cpu NMI buffer too,
and use that if "in_nmi()" is true.

-- Steve


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